netdev - Re: [PATCH take 2] pkt_sched: Fix qdisc_watchdog() vs. dev

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Message-ID: <20080911115132.GA5765@ff.dom.local>
Date:	Thu, 11 Sep 2008 11:51:32 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH take 2] pkt_sched: Fix qdisc_watchdog() vs.
	dev_deactivate() race

On Thu, Sep 11, 2008 at 09:00:35PM +1000, Herbert Xu wrote:
> On Thu, Sep 11, 2008 at 03:49:55AM -0700, David Miller wrote:
> > 
> > Well some kind of check has to be there.
> > 
> > I _did_ remove it during my initial implementation, and that
> > turned into a reported performance regression.
> 
> I see.  How about looking at the queue that the head-of-qdisc
> packet maps to? That should be fairly cheap to compute.
> 

Very good point: "That can't be right"! But I'm not sure I got the
above idea: e.g. this new sch_multiq can have different packets
depending just on some unstopped tx_queue.

IMHO, the most reasonable test here is for all tx_queues of a qdisc
beeing stopped, but since this is quite heavy, probably we need an
additional qdisc flag for such an occasion.

Jarek P.
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